1. Field of the Invention
The present invention relates to a combination of a cutter such as, for example, a face milling cutter and a fastener unit for fastening the cutter to a tool attachment shaft such as, for example, an arbor for a machine tool.
2. Prior Art
FIGS. 1 and 2 of the accompanying drawings depict one conventional combination of a cutter and a fastener unit therefor hitherto known. The cutter includes a cutter body 2 adapted to be fastened to a forward end of a tool attachment shaft or an arbor 1 by means of a fastener unit including a bolt 3. A plurality of cutter inserts 4 are mounted on an outer periphery of a forward end of the cutter body 2 in circumferentially equidistantly spaced relation to each other. The body 2 is formed at its center with a through bore 2a through which the bolt 3 passes. A rearward end face of the cutter body 2 is formed at its center with a recess 2b into which a projection 1a on a forward end face of the arbor 1 is fitted. The forward end face of the cutter body 2 is formed at its center with a counterbore 2c in which a head of the bolt 3 is accommodated.
It is essential for the above conventional arrangement to form the counterbore 2c in the forward end face of the body 2, in order to prevent the head of the bolt 3 from protruding forwardly from the cutter inserts 4. Provision of such counterbore 2c reduces the area of the forward end face of the body 2, resulting in such a defect that it is difficult to secure sufficient regions for attachment of clamp screws for the inserts 4, to the cutting body 2. Because of the defect, there arise such problems that it is not easy to design the regions where the clamp screws are attached, and that provision of threaded bores, with which the clamp screws are threadedly engaged, in the narrow regions reduces the rigidity of the cutter body 2, resulting in a deterioration of the cutting performance of the cutter.
Another conventional arrangement shown in FIGS. 3 and 4 is also known from Japanese Patent Publication No. 60-3538. A plurality of cutter inserts 13 are mounted on an outer periphery of a forward end face of a cutting body 12 in circumferentially spaced relation to each other. The cutter body 12 is formed at its center with a stepped through bore composed of a large-diameter bore section 12a, a small-diameter bore section 12b and a recess 12c, which are arranged in the mentioned order from a rearward end face of the body 12 facing toward a forward end face of an arbor 11. The large-diameter bore section 12a has such an accurate and precise inner diameter that an axial projection 11a on the forward end face of the arbor 11 can be fitted into the large-diameter bore section 12a. As shown in FIG. 4, a pair of diametrically opposed axial grooves 12d and 12d are formed in the peripheral wall surface of the small-diameter bore section 12b. The cutter body 12 is adapted to be fastened to the forward end of the arbor 11 by means of a clamper 14 and a bolt 15.
The clamper 14 is generally cylindrical in shape, and a pair of diametrically opposed projections 14a and 14a extend radially outwardly from an outer peripheral surface of one axial end of the clamper 14. Each of the pair of projections 14a is formed into a size capable of passing through a corresponding one of the pair of axial grooves 12d and 12d in the body 12. The clamper 14 is mounted on the bolt 15 in such a manner that the clamper 14 is urged against a head 15a of the bolt 15 under biasing force of a spring washer 16 which is fitted around the shank of the bolt 15 so as to be interposed between the clamper and the threaded portion of the bolt.
For fastening the cutter body 12 to the arbor 11, the bolt 15 having the clamper 14 mounted thereon is first screwed into the arbor 11. The spacing between the end face of the projection 11a on the arbor 11 and axial end faces of the respective projections 14a and 14a on the clamper 14, which face toward the end face of the projection 11a, is brought to a value slightly larger than the axial thickness of arcuate sections of the cutter body 12 extending between the pair of axial grooves 12d and 12d, i.e., the axial length of the small-diameter bore section 12b. In this state, the cutter body 12 is arranged in front of the head of the bolt 15, and the pair of axial grooves 12d and 12d in the cutter body 12 are axially aligned respectively with the pair of projections 14a and 14a on the clamper 14. The cutter body 12 is then moved toward the forward end face of the arbor 11, while the pair of projections 14a and 14a move respectively in and along the pair of axial grooves 12d and 12d. The projection 11a on the arbor 11 is fitted into the large-diameter bore section 12a in the cutter body 12. Subsequently, the cutter body 12 is moved angularly about the axis thereof relatively to the clamper 14 to a position where the arcuate sections between the axial grooves 12d and 12d in the cutter body 12 are located between the respective projections 14a and 14a on the clamper 14 and the projection 11a on the arbor 11 and are overlapped respectively with the projections 14a and 14a. As the bolt 15 is tightened, the arcuate sections between the axial groves 12d and 12d in the cutter body 12 are urged respectively by the projections 14a and 14a on the clamper 14 so that the cutter body 12 is fixedly fastened to the arbor 11.
On the other hand, when it is desired to remove the cutter body 12 from the arbor 11, the bolt 15 is first loosened. The clamper 14 is moved together with the head of the bolt 15 under the action of the spring member 16 so that the projections 14a and 14a on the clamper 14 move away from the respective arcuate sections between the axial grooves 12d and 12d in the cutter body 12. Subsequently, the cutter body 12 is moved angularly about the axis thereof relatively to the clamper 14 to bring the axial grooves 12d and 12d into alignment with the respective projections 14a and 14a on the clamper 14. The cutter body 12 is then moved away from the forward end of the arbor 11, and is removed therefrom.
Still another conventional arrangement shown in FIG. 5 is also known from Japanese Patent Publication No. 60-165. The arrangement shown in FIG. 5 is similar to that illustrated in FIGS. 3 and 4, but is different from the latter in that a spring member 17 is arranged between the clamper 14 and the arbor 11. The clamper 14 is urged against the head of the bolt 15 under the biasing force of the spring member 17. As the bolt 15 is loosened when the cutter body 12 is fixedly fastened to the arbor 11, the projections 14a on the clamper 14 move away from the respective arcuate sections between the axial grooves 12d and 12d in the cutter body 12. A recess 14b is formed at a center of the forward end face of the clamper 14 so as to prevent the head of the bolt 15 from protruding outwardly from the plane including the cutter inserts 13.
As described above, in the conventional arrangement illustrated in FIGS. 3 and 4 or FIG. 5, the spring member 16 or 17 is provided for urging the clamper 14 against the head of the bolt 15 so as to prevent the clamper 14 from moving between the forward end face of the arbor 11 and the head of the bolt 15, thereby facilitating attachment and detachment of the cutter body 12 to and from the arbor 11. In this manner, the spring member 16 or 17 is required for the conventional arrangement, and portions associated with the spring member 16 or 17 are complicated in construction inevitably. This results in an increase in the cost.
Moreover, the recess 12c is formed in the forward end face of the cutter body 12 as shown in FIG. 3, or the recess 14b is formed in the forward end face of the clamper 14 as shown in FIG. 5, in order to prevent the head of the bolt 15 from protruding outwardly from the plane including the cutter inserts 13. Because of the provision of such recess 12c or 14b, such a problem arises that the rigidity of the cutter body 12 or the clamper 14 is reduced.